Several types of impeller pumps, used for providing continuous power to move liquids, are known to those skilled in the art. In the typical impeller pumps, a blade, gear, screw or cam-type impeller or runner is rotatably arranged in a pump casing, thus being capable of forcibly moving liquids, such as oil or water, under pressure. However, the known impeller pumps are problematic in that the moving distance of a runner is too long to conserve power during every pumping cycle. In addition, the runner of a known impeller pump also comes into contact with violent vortex or turbulent flow of liquid at an exceedingly large contact area during a pumping operation, thus overly consuming power. Such a contact between the runner and the violent vortex or turbulent flow of liquid also generates frictional heat and consumes the runner due to frictional abrasion, thereby preventing the pump from being operated at a high speed and reducing the expected life span of the pump.
Another problem experienced in each of the above impeller pumps is that both a runner and a runner chamber of a pump casing have a complex construction, thus being limited in their design flexibility and use.
Korean Patent Publication No. 91-4769 and Japanese Patent Appln. No. Sho. 63-126511 individually disclose a rotary compressor. In each of the above rotary compressors, one cylindrical rotor or runner is eccentrically arranged in the rotor chamber of a compressor casing and is eccentrically rotated in the chamber, thus compressing liquids prior to moving the liquids. However, the moving distance of the above rotor is too long to effectively accomplish desired operational efficiency of the compressor during an operation. In addition, the above rotary compressors individually require a plurality of spring-biased thin blades and a check valve, with the check valve being used for preventing unexpected reverse flow of liquids from a discharge port during a suction stroke of the rotor. Therefore, the rotary compressors have a complex construction with a plurality of delicate and vulnerable points, which prevent the compressors from being operated at a high speed and high pressure and reduce the expected life span of the compressors.
Korean Patent Publication No. 90-3682 and Japanese U.M. Appln. No. Sho. 61-178289 individually disclose a vane pump with a plurality of spring-biased thin blades. However, each of the above vane pumps has the same problems as that described for the above rotary compressors due to the thin blades.
Korean Patent Publication No. 89-628 and Japanese Patent Appln. No. Sho. 59-222753 individually disclose a scroll-type hydraulic machine. Each of the above hydraulic machines has a complex scroll structure, which includes a plurality of specifically designed involute and arcuate curves. However, such a complex scroll structure makes the production of the hydraulic machines very difficult and increases the manufacturing cost of the machines. In the operation of the above hydraulic machines, pressurized liquid is sucked into and discharged from a machine through variable liquid chambers, which are formed by the movable and stationary scrolls and individually have a small area. Therefore, the hydraulic machines regrettably limit the amount of sucked and discharged liquid during one rotation of the movable scroll relative to the stationary scroll.
In an effort to effectively overcome the above problems, the inventor of this invention proposed a twin-cylinder impeller pump with a twin cylinder runner in Korean Patent Appln. No. 94-10299. The above impeller pump has a simple and effective construction, thus being easily produced and having improved pump efficiency and being effectively used for various applications. FIGS. 1 and 2 show the construction of the above impeller pump. As shown in the drawings, the twin cylinder runner is comprised of two cylinder impellers, that is, first and second cylinder impellers 103 and 104 integrated into a single structure by a web. The two cylinder impellers 103 and 104, having the same size and configuration, are eccentrically fitted over two shafts 112 and 113 with bearings and are rotatable around the shafts 112 and 113 in opposite directions while maintaining the same eccentricity. The two shafts 112 and 113 are eccentrically connected to two eccentric transmission gears 116 and 117, which have the same size and eccentricity and engage with each other. When the twin cylinder runner is moved in a pump casing with the two cylinder impellers 103 and 104 being eccentrically rotated around the shafts 112 and 113, the interval between the center of each cylinder impeller 103, 104 and the center of an associated shaft 112, 113 is almost completely maintained. The two cylinder impellers 103 and 104 are eccentrically received in two cylindrical chambers 105 and 106 of the pump casing, thus being slidably inscribed with the chambers 105 and 106 respectively. The two chambers 105 and 106, having the same size and configuration, are symmetrically formed in the casing with an intermediate throat being formed between the two chambers 105 and 106 and communicate with each other through an opening formed at the intermediate throat of the casing. A suction port 107 is formed at one side wall of the throat of the casing, while a discharge port 108 is formed at the other side wall of the throat at a position opposite to the suction port 107. The two cylinder impellers 103 and 104 are integrated with each other into a single structure by a web. The web of the twin cylinder runner is also used as a partition wall since the web isolates the two ports 107 and 108 from each other.
In the above twin-cylinder impeller pump, the two cylinder impellers 103 and 104 and the chambers 105 and 106 individually have a genuine cylindrical configuration. In addition, the above impeller pump is also free from any delicate moving points except for the two cylinder impellers 103 and 104 integrated into a single structure by the web. Therefore, the above pump has a simple construction suitable for being easily produced and being effectively used for a lengthy period of time without breaking down. The two cylinder impellers 103 and 104, having a genuine cylindrical configuration, smoothly slide on the internal surfaces of the chambers 105 and 106 while alternately sucking and discharging pressurized liquid relative to the chambers 105 and 106, thus being almost free from the formation of any pulsation. The above impeller pump reduces the moving distance of the runner and remarkably reduces the contact area between the runner and the pressurized liquid, and causes neither violent vortex nor turbulent flow of liquid, thus conserving power and being somewhat effectively operated at a high speed and high pressure.
However, the above twin-cylinder impeller pump is problematic in that when the twin cylinder runner is positioned at its upper or lower dead point, a gap is formed between one of the two cylinder impellers 103 and 104 and the side wall of an associated chamber 105, 106 at a position "S" around the throat of the pump casing as shown in FIG. 2. The above gap allows pressurized liquid to pass through during a pumping operation, thus causing a pressure loss of the pump. Another problem of the above impeller pump is caused by the eccentric transmission gears 116 and 117. That is, the two shafts 112 and 113 are eccentrically connected to the gears 116 and 117 as described above and so the shafts 112 and 113 may reduce operational efficiency of the pump. In addition, when the twin cylinder runner is positioned outside the upper or lower dead point, the interval between the two shafts 112 and 113 becomes longer and may cause an operational problem of the pump. The above impeller pump is thus designed to maintain a contact interval between the two shafts 112 and 113 irrespective of positions of the twin cylinder runner in the pump casing. That is, the two shafts 112 and 113 are eccentrically connected to the eccentric gears 116 and 117, respectively. However, such eccentric gears have different angular velocities and so they may engage with each other with excessive interference at their mating portions perpendicular to the eccentric direction. In such a case, the two gears are excessively interfered with each other and fail to be smoothly operated. In order to overcome such an interference between the two eccentric gears, the two gears 116 and 117 of the above impeller pump are provided with a large backlash between them. However, such a large backlash causes operational noises and vibrations of the gears 116 and 117.